The present invention relates to an electrophotographic photosensitive material having a photosensitive layer composed of an amorphous silicon-based material and a protective layer formed from hydrogen and fluorine containing amorphous carbon.
Photoconductive materials utilizing amorphous silicon containing hydrogen as a matrix material, e,g,, hydrogenated amorphous silicon (a-Si(H)) produced by glow discharge or photo CVD of silane gas (SiH.sub.4) have excellent photosensitivity, heat resistance and printing durability, and may be comparatively easily made into a thin film of a great surface area. Furthermore, such films can be formed with little or no fear of environmental contamination. Therefore, amorphous silicon containing hydrogen has recently been attracting attention as a photoconductive material for electrophotographic photosensitive materials.
However, electrophotographic photosensitive materials utilizing such a-Si(H) layer as the surface layer have been frequently found to form poor images when copying is conducted after storage in air or in high humidity for a prolonged time, although they initially give good images. Further, it has been found that prolonged utilization of such photosensitive materials in a copying process gradually causes blurring of the image. Particularly, such heavily used and deteriorated photosensitive materials tend to generate blurring in the image in high humidity, and it has already been confirmed that the critical humidity at which blurring in the image begins to be generated decreases as the number of images copied with the material is increased.
It is presumed that the photosensitive material utilizing a-Si(H) as the surface layer is susceptible to influences on the outermost surface of the photosensitive material by being exposed to air or moisture for a prolonged time or by a chemical species (e,g, ozone, nitrogen oxides, nascent oxygen etc.) generated by corona discharge etc. in the copying process and produces poor images as a result of some chemical change in the properties, but the mechanism of deterioration has not been satisfactorily studied yet. In order to prevent the generation of such poor images and to enhance the printing durability, methods which provide the surface of an a-Si(H) photosensitive material with a protective layer for chemically stabilization have been tried.
For example, a method for preventing the deterioration of a surface layer of a photosensitive material due to a copying process or an environmental atmosphere is known in which hydrogenated amorphous silicon carbide (a-Si.sub.x C.sub.l-x (H) 0&lt;X&lt;1) or hydrogenated amorphous silicon nitride (a-Si.sub.x N.sub.l-x (H)0(X)&lt;1) is utilized as a surface protective layer (Japanese Patent Application Laid-open No. 115559/1983 Official Gazette). However, although the printing durability can be considerably improved by selecting the carbon concentration or nitrogen concentration in the surface protective layer at an optimum value, it is impossible to maintain the moisture resistance in a highly humid atmosphere (RH 80% or higher). Furthermore, blurred images are formed by these materials at a relative humidity on the order of 60% when the material has been used for copying several ten thousand sheets. Thus, even if a surface protective layer is provided thereon, it has not been possible to greatly enhance the printing durability and the moisture resistance of a-Si(H) photosensitive materials.
It is therefore an object of the present invention is to provide an a-Si based photosensitive material having excellent durability, printing durability and moisture resistance, which eliminates the above-described drawbacks and having characteristics which are stable. It is a further object of the invention to provide photosensitive material that is not restricted as to the atmosphere in which it can be used. Further, it is an object of the invention to provide photosensitive material that does not suffer from deterioration even on long-term storage or repeated use and that suffers from almost no reduction in the characteristics such as image quality etc. in a highly humid atmosphere.